4 ms·

The definition of wear out is more than just the SSD declaring the cell bad, or the SSD failing suddenly. A cell is technically declared worn out when the cha

by tytso 12y ago

The definition of wear out is more than just the SSD declaring the cell bad, or the SSD failing suddenly. A cell is technically declared worn out when the chance that the cell suffer charge leakage after N months at temperature T exceeds probability P. (Where exactly what these parameters are are a secret that the SSD vendors don't disclose. There are some standards, but the SSD vendors don't necessarily use those standards when the make promises about their product's wear endurance. So even though an SSD might last for 1.5 PB's worth of writes, there is no guarantee that if you were to then put the SSD on a shelf and wait nine months, that they data will still be good. This is probably one some vendors will declare themselves to be dead after so many gigabytes worth of writes, even if the flash cells haven't "failed" yet. Otherwise users might depend on the SSD's contents being retained, when in fact they might suffer data loss. But of course, this doesn't really matter much, because you treat all data stored on SSD's as a cache, and do regular backups, RIGHT? :-)

camillomiller 12y ago
Of course, on magnetic tapes!
- allegory 12y ago
  I still use a Quantum VS160 DLT to back up my SSD... The thing plugs straight into my laptop via no brand cheapo SCSI/USB bridge much to the laughing from my colleagues (apart from the ops team who understand why I do it). Being an ex EE, I understand exactly how "transient" the state of an SSD is. Electrons; gotta catch 'em all.
  - beagle3 12y ago
    Is it because you are not a CE that you don't understand how transient DLT tapes are? Some people have experienced 10% failure/year and discovered it has to do with storage orientation.
    - kjs3 12y ago
      What does Civil Engineering have to do with tape reliability? I back up to tape as well (write+verify). It's a risk mitigation strategy (as well as a cost savings). I don't expect to read the tape 10 years from now; I expect to read it an hour or so after a drive fails. The 3 or 4 times I've had to rely on this strategy, I've never lost data.
      - beagle3 12y ago
        I meant chemical engineering. Not versed in all the acronyms, I apologize. Despite the commonly believed myths, tapes are not very durable unless you store them in the right temperature and humidity and the right orientation. And .. what do you know, the same holds true for magnetic drives (with slightly different, though no harder to achieve, environmental conditions). Tapes are also generally more expensive before the 200TB mark or so these days (you did factor the cost of a drive into your cost saving, did you?) and actually around 400TB if you factor in two drives (which you should, because the tape drive also fails). Trusting an SSD is stupid. But the economics of backup tapes are very different from what the vast majority of people believe. For 99.9% of the situations, backing up to a magnetic drive is a better solution.
bloat 12y ago
This does not invalidate your point of course, but note that the article describes one of the tests some of these drives have passed: write a large file and power the drive off for a week and then check the file.
- allegory 12y ago
  Try powering off for 5 years and keeping at 75oC and see if the data is still there.
  - gambiting 12y ago
    Wouldn't most storage types, including regular hdds and optical media fail this test though? I am not talking about complete data loss, but some data would be corrupted after such time.
    - allegory 12y ago
      Decent quality hard disks and DLTs will probably be fine. I've had DLTs survive 100oC for over an hour inside a fire safe in a fire and some old Seagate Cheetah 10K U160 SCSI disks in an external SCSI case with a dead fan running at 80oC for a month quite happily. The latter was actually running and operational which is remarkable. Some optical media will fail. It doesn't even have to be kept at 75oC from experience. Flash will almost certainly fail (leakage increases with temperature). I've had dead CF cards, USB sticks, SD cards, the lot and corruption after only a couple of years stored in ideal conditions. Then there's the old Sun PROM crapfest to consider as well... These are all anecdotes, but there is data out there to support this as well.
      - VLM 12y ago
        "I've had dead CF cards, USB sticks, SD cards, the lot and corruption after only a couple of years stored in ideal conditions. Then there's the old Sun PROM crapfest to consider as well." The story goes back much further with solid state if you talk to "retrocomputing enthusiasts" unfortunately eproms reading all 1 awhile is depressingly common. You only need a single bit error of course for software failure. Another interesting point to bring up is it is Very well known in the retro community that the details of eprom programming technique and certification (or lack thereof) of eprom programers has a dramatic effect on burn lifetime, like multiple orders of magnitude difference in burn lifetime. Anyone can make an eprom burner that verifies an hour later. Much harder to make an eprom burner that verifies 10 years later. This affects more than stereotypical retrocomputing due to embedded devices. Plenty of PBXes and machine tool controllers and scientific instruments and classic video arcade machines get scrapped because the eproms lost their minds.
brazzy 12y ago
> treat all data stored on SSD's as a cache, and do regular backups, RIGHT? You meant: all data stored anywhere, RIGHT? The best way I've heard it put: data that is not backed up is implicitly classified as "nice to have".
ilaksh 12y ago
"all data stored on SSDs as a cache" is absolutely wrong. The SSD reliability is not less when compared to HDDs. The SSD is just as useful as permanent storage as an HDD. Each SSD drive must be evaluated individually. Some batches or models are very unreliable. This can still be an issue with HDDs however. All storage without backups is subject to loss, therefore all storage systems require backups of important data. RAID and other redundant systems can reduce the likelihood of data loss in SSDs just as well as HDDs. If you statement was that all SSD data must be backed up regularly, just as HDD data is, then it would have been correct. As you stated it, incorrect and misleading.

by tytso 12y ago

camillomiller 12y ago

Of course, on magnetic tapes!

allegory 12y ago
I still use a Quantum VS160 DLT to back up my SSD... The thing plugs straight into my laptop via no brand cheapo SCSI/USB bridge much to the laughing from my colleagues (apart from the ops team who understand why I do it). Being an ex EE, I understand exactly how "transient" the state of an SSD is. Electrons; gotta catch 'em all.
- beagle3 12y ago
  Is it because you are not a CE that you don't understand how transient DLT tapes are? Some people have experienced 10% failure/year and discovered it has to do with storage orientation.
  - kjs3 12y ago
    What does Civil Engineering have to do with tape reliability? I back up to tape as well (write+verify). It's a risk mitigation strategy (as well as a cost savings). I don't expect to read the tape 10 years from now; I expect to read it an hour or so after a drive fails. The 3 or 4 times I've had to rely on this strategy, I've never lost data.
    - beagle3 12y ago
      I meant chemical engineering. Not versed in all the acronyms, I apologize. Despite the commonly believed myths, tapes are not very durable unless you store them in the right temperature and humidity and the right orientation. And .. what do you know, the same holds true for magnetic drives (with slightly different, though no harder to achieve, environmental conditions). Tapes are also generally more expensive before the 200TB mark or so these days (you did factor the cost of a drive into your cost saving, did you?) and actually around 400TB if you factor in two drives (which you should, because the tape drive also fails). Trusting an SSD is stupid. But the economics of backup tapes are very different from what the vast majority of people believe. For 99.9% of the situations, backing up to a magnetic drive is a better solution.

bloat 12y ago

This does not invalidate your point of course, but note that the article describes one of the tests some of these drives have passed: write a large file and power the drive off for a week and then check the file.

allegory 12y ago
Try powering off for 5 years and keeping at 75oC and see if the data is still there.
- gambiting 12y ago
  Wouldn't most storage types, including regular hdds and optical media fail this test though? I am not talking about complete data loss, but some data would be corrupted after such time.
  - allegory 12y ago
    Decent quality hard disks and DLTs will probably be fine. I've had DLTs survive 100oC for over an hour inside a fire safe in a fire and some old Seagate Cheetah 10K U160 SCSI disks in an external SCSI case with a dead fan running at 80oC for a month quite happily. The latter was actually running and operational which is remarkable. Some optical media will fail. It doesn't even have to be kept at 75oC from experience. Flash will almost certainly fail (leakage increases with temperature). I've had dead CF cards, USB sticks, SD cards, the lot and corruption after only a couple of years stored in ideal conditions. Then there's the old Sun PROM crapfest to consider as well... These are all anecdotes, but there is data out there to support this as well.
    - VLM 12y ago
      "I've had dead CF cards, USB sticks, SD cards, the lot and corruption after only a couple of years stored in ideal conditions. Then there's the old Sun PROM crapfest to consider as well." The story goes back much further with solid state if you talk to "retrocomputing enthusiasts" unfortunately eproms reading all 1 awhile is depressingly common. You only need a single bit error of course for software failure. Another interesting point to bring up is it is Very well known in the retro community that the details of eprom programming technique and certification (or lack thereof) of eprom programers has a dramatic effect on burn lifetime, like multiple orders of magnitude difference in burn lifetime. Anyone can make an eprom burner that verifies an hour later. Much harder to make an eprom burner that verifies 10 years later. This affects more than stereotypical retrocomputing due to embedded devices. Plenty of PBXes and machine tool controllers and scientific instruments and classic video arcade machines get scrapped because the eproms lost their minds.

brazzy 12y ago

> treat all data stored on SSD's as a cache, and do regular backups, RIGHT? You meant: all data stored anywhere, RIGHT? The best way I've heard it put: data that is not backed up is implicitly classified as "nice to have".

ilaksh 12y ago

"all data stored on SSDs as a cache" is absolutely wrong. The SSD reliability is not less when compared to HDDs. The SSD is just as useful as permanent storage as an HDD. Each SSD drive must be evaluated individually. Some batches or models are very unreliable. This can still be an issue with HDDs however. All storage without backups is subject to loss, therefore all storage systems require backups of important data. RAID and other redundant systems can reduce the likelihood of data loss in SSDs just as well as HDDs. If you statement was that all SSD data must be backed up regularly, just as HDD data is, then it would have been correct. As you stated it, incorrect and misleading.